Put a gun in the hand of someone who is stupid or has mental issues, you have a problem, and it isn't the gun.
Unfortunately these parents fucked up beyond belief. They didn't follow safety procedures correctly and their entire family is going to pay for it. Makes it even more unfortunate because the reason you give a 5 year old a rifle is so that you can take them to the range and teach them how to handle and use it properly and safely. Children learn things better than adults do. They are still pulling in information 24 hours a day trying to fill up an empty database in their head, it is the right time to start giving them the information to store.
As I said in another thread, up until around the 60's or 70's it was the norm for a kid around 5-10 to get a rifle, and learn how to use it. It was actually a right of passage the same way getting a pocket knife was a right of passage. And you didn't see a wave of children offing other people or themselves with guns and knives.
Once again as I said in another thread the major problem here is that people used to understand how to use a tool the way it was meant to be used and now most people are just tools themselves.